It has been recognized virtually from the beginning of studies of electrical phenomenon that electrical components can be destroyed by over current or overvoltage conditions and a variety of prophylactic measures have been taken to ameliorate or to avoid damage to electrical components since their first use. One cause of an overvoltage condition is a rapid rate of changing the magnitude of current because of inductive affects being present in the circuit in which the current magnitude is being changed (overshoot overvoltage).
The motor controller of the present invention is a pulse width modulated controller for adjusting the amount and frequency of power provided to a motor. Motor controllers and pulse width modulated motor controllers, as such, are also known. The present invention includes a way of detecting a fault condition in the controller or the motor and avoid attempts to rapidly change the current level which would result in an overshoot overvoltage fault. A number of schemes are known which attempt to or do reduce the likelihood of overvoltage conditions under varying circumstances.
Among publications describing aspects of such generally known, or related, schemes are the following patents:
U.S. Pat. No. 4,528,494 issued to Bloomer on Jul. 9, 1985 for a REVERSE-PHASE-CONTROL POWER SWITCHING CIRCUIT AND METHOD.
U.S. Pat. No. 4,543,522 issued to Moreau on Sep. 24, 1985 for a REGULATOR WITH A LOW DROP-OUT VOLTAGE.
U.S. Pat. No. 4,639,616 issued to Gaude on Jan. 27, 1987 for a CIRCUIT FOR CONTROLLING THE BASE OF A POWER TRANSISTOR USED IN HIGH TENSION SWITCHING.
U.S. Pat. No. 4,697,218 issued to Nicolas on Sep. 29, 1987 for an OVERCURRENT PROTECTION DEVICE.
U.S. Pat. No. 4,771,357 issued to Lorincz et al on Sep. 13, 1988 for a POWER DRIVER HAVING SHORT CIRCUIT PROTECTION.
U.S. Pat. No. 4,792,747 issued to Schroeder on Dec. 20, 1988 for a LOW VOLTAGE DROPOUT REGULATOR.
U.S. Pat. No. 4,827,366 issued to McNally et al on May 2, 1989 for a BI-POLAR POWER SUPPLY REGULATOR BI-POLAR POWER SUPPLY REGULATOR.
U.S. Pat. No. 4,864,214 issued to Billings et al on Sep. 5, 1989 for SOLID STATE POWER CONTROLLER.
U.S. Pat. No. 4,891,728 issued to Preis et al on Jan. 2, 1990 for a CIRCUIT ARRANGEMENT FOR LIMITING THE SWITCH-ON CURRENT AND FOR PROVIDING AN OVER VOLTAGE PROTECTION IN SWITCH MODE POWER SUPPLY DEVICES.
It is believed that Fuji Electric Company may have placed a protective device under their model no. EXB-721 IGBT into the public domain more than one year before the filing of this application.
The motor controller of the present invention is believed to reliably function over the entire range of potential fault conditions experienced by the motor controller.